Molecular reaction networks that reveal the various reaction possibilities of a system are of vital importance for chemistry and biochemistry. The molecular origins of life are a prime example of branched networks. We need only recall the famous “primordial soup” experiment (Miller-Urey experiment) of 1953 on the emergence of organic molecules in the Earth’s early atmosphere or consider the formation of molecules in interstellar space. Understanding, predicting, and ultimately calculating such reaction networks is a highly complex task. With the development of a so-called hyperreactor, the team led by Christian Ochsenfeld, CeNS member and Professor of Theoretical Chemistry at LMU, is pursuing this ambitious goal.

Using the tools of theoretical chemistry, it is possible to simulate such reaction networks. A key challenge is presented by the complexity of the potential energy hypersurfaces of chemical systems, with numerous minima and connecting saddle points. The latter constitute energy barriers which a chemical reaction must overcome. Simplifying matters, we can picture this potential energy hypersurface as a mountainous terrain, where various molecules or structures correspond to the valleys and the energy barriers to be overcome are represented by the mountains.

The difficulty posed by the energy barriers, which are often very high, were circumvented in early approaches by means of simulation under periodic contractions (pressure) and very harsh reaction conditions such as extremely high temperatures to induce chemical reactions. However, this has also led to unrealistic reactions and fragmentations. By contrast, the new hyperreactor from the Ochsenfeld group enables the study of complicated reaction networks under mild conditions. To this end, periodic contractions of the molecular system are coupled with the exploration of chemical space on smoothed potential energy surfaces.

Sample applications of the hyperreactor – such as the calculation of nonenzymatic DNA nucleoside synthesis, which is being experimentally researched in the group led by Oliver Trapp, Professor of Organic Chemistry at LMU, or the synthesis of glycinal, acetamide, and carbamic acid in interstellar ices at -263°C – are yielding initial insights into the new computational possibilities. Particularly when combined with new, almost 1,000 times faster quantum chemical methods, which were also developed in Ochsenfeld’s research group, the hyperreactor opens up new perspectives for the exploration of complex reaction networks and for research into a wide variety of chemical and biochemical synthesis pathways.

Publication: Alexandra Stan-Bernhardt, Liubov Glinkina, Andreas Hulm, Christian Ochsenfeld: Exploring Chemical Space Using Ab Initio Hyperreactor Dynamics; ACS Central Science 2024

Source: LMU Munich